MODELING OF RETROGRADATION OF WAXY AND NORMAL CORN STARCHES

Retrogradation behavior of waxy and normal corn starch gels stored at 5 and 21 C were investigated for 50 days by differential scanning calorimetry. The extend of retrogradation can be expressed as the ratio of retrogradation and gelatinization enthalpy values and these were 70-78% for normal corn starch and 39-68% for amioca stored at two temperatures. Higher retrogradation rates were observed at 5 degrees C for both waxy and normal corn starch. Kinetic data were evaluated by considering retrogradation as consecutive reactions in series and by Avrami Equation. High R-2 values (0.97-0.98) indicated that both models can be used for prediction. The comparison of rate constants obtained by Avrami Equation indicated that both temperature and amylose content of starch affected the recrystallization rate. By the kinetic model based on consecutive reactions in series, it was proven mathematically that the rate limiting step in recrystallization of starch gels is the nucleation.